cannot create a local file using await getApplicationDocumentsDirectory(); - flutter

Question

when I run the following function
_makeFile() async{
final dataFile = 'data.txt';
final directory = await getApplicationDocumentsDirectory();
final file = File('${directory.path}/$dataFile');
var isExist = await file.exists();
if (isExist) {
print('File exists');
} else {
print('file does not exist');
}
}
I get :
flutter: file does not exist
Flutter doctor :
jfb # ezer in ~/FTest/file_exist [12:16:41]
$ flutter doctor -v
[✓] Flutter (Channel stable, v1.12.13+hotfix.5, on Mac OS X 10.15.2 19C57, locale en-FR)
• Flutter version 1.12.13+hotfix.5 at /usr/local/flutter
• Framework revision 27321ebbad (4 weeks ago), 2019-12-10 18:15:01 -0800
• Engine revision 2994f7e1e6
• Dart version 2.7.0
[!] Android toolchain - develop for Android devices (Android SDK version 28.0.3)
• Android SDK at /Users/jfb/Library/Android/sdk
• Android NDK location not configured (optional; useful for native profiling support)
• Platform android-28, build-tools 28.0.3
• Java binary at: /Library/Java/JavaVirtualMachines/jdk-10.0.2.jdk/Contents/Home/bin/java
• Java version Java(TM) SE Runtime Environment 18.3 (build 10.0.2+13)
! Some Android licenses not accepted. To resolve this, run: flutter doctor --android-licenses
[✓] Xcode - develop for iOS and macOS (Xcode 11.3)
• Xcode at /Applications/Xcode.app/Contents/Developer
• Xcode 11.3, Build version 11C29
• CocoaPods version 1.8.3
[!] Android Studio (not installed)
• Android Studio not found; download from https://developer.android.com/studio/index.html
(or visit https://flutter.dev/setup/#android-setup for detailed instructions).
[✓] Connected device (1 available)
• iPhone 11 Pro Max • 1669648E-FBC3-41D7-9DA0-8E4FF5EBB360 • ios •
com.apple.CoreSimulator.SimRuntime.iOS-13-3 (simulator)
! Doctor found issues in 2 categories.
I just do not understand what's happening, I used this approach in order to store json without problem
Thanks for any pointer ...
JF

Answer 1

This line :
final file = File('${directory.path}/$dataFile');
does not create a File but only a reference.
To create a File, you need to use writeAsString() or writeAsBytes().
Retry by adding :
final dataFile = 'data.txt';
final directory = await getApplicationDocumentsDirectory();
final file = File('${directory.path}/$dataFile');
await file.writeAsString('This is data.txt content'); // <-- This line
print(await file.exists() ? 'Exists' : 'Do not exists');